CDA is not a file itself - it is stub virtual file, always 44 bytes in size, created by Windows for access tracks on CD. This file can't be converted online as physical access to CD-ROM has to be gained. More information about CDA files can be found in Wikipedia article.
So, we can't and don't support CDA file, unfortunately. We do support CDDA files, with which some users may confuse CDA.
The full list of the file types supported by us can be found here.